and dvd/bray never fail? i have brand name discs from 10 years ago that fail in some drives (not all), and others from even longer back that are kaput in all drives.
usb/hard drives might fail, but backing up files to numerous drives is not only a sensible precaution but, especially commercially, a no-brainer. not only do i have my files backed up to numerous drives (stored in different locations), but also on the cloud.
most people i know who've bought laptops in the last few years have opted (when there was a dvd installed) to have it removed and a second large capacity hd installed instead (the boot drive usually being a relatively small ssd). of course, ymmv.
in maybe a few years or so dvd/bray drives will be even scarcer to find in off the shelf equipment, and in 10, well, i don't see them making a comeback like vinyl
as for actual storage capacity, if you have a LOT of material, mpg for dvd even at high bitrate isn't the optimum format, eg. and hour or so on a dvd, and a real pain cataloging dozens of them for easy access.
as for usb/hd drives failing, i'll take my chances against a dvd becoming unreadable, whether from material deterioration, or my grandkids playing frisbee with it, or simply getting scratched.